Article comprising optical fiber having low polarization mode dispersion, due to permanent spin

Abstract

The presence of (typically unintended) birefringence in single mode optical fiber can severely limit the usefulness of the fiber for, e.g., high bit rate or analog optical fiber communication systems, due to the resulting polarization mode dispersion (PMD). It has now been discovered that PMD can be substantially reduced if, during drawing of the fiber, a torque is applied to the fiber such that a "spin" is impressed on the fiber. Desirably the torque is applied such that the spin impressed on the fiber does not have constant spatial frequency, e.g., has alternately clockwise and counterclockwise helicity. At least a portion of optical fiber according to the invention has spin alternately clockwise and counterclockwise.

We claim: 
     
       1. An article comprising optical communication fiber with a spin impressed on the fiber; CHARACTERIZED IN THAT the fiber is single mode optical fiber; and in at least a portion of the fiber the spin impressed on the fiber is alternately clockwise and counterclockwise, with a spin repeat distance of at most 20 m. 
     
     
       2. Article according to claim 1, wherein said single mode optical fiber has a polarization mode dispersion (PMD), with the PMD of the fiber being less than 0.5 ps/km 1/2 . 
     
     
       3. Article according to claim 2, wherein the article is an optical communication system that comprises an optical signal source a length of optical fiber comprising said single mode optical fiber and an optical signal detector, with said length optical fiber signal-transmissively connecting said source and said detector. 
     
     
       4. Article according to claim 1, wherein the repeat distance is at most 13.2 m.